In 1911,
the Stevens Motor Manufacturing Company, founded at the turn of the century by
the four Stevens brothers - who had been supplying V-twin engines to Clyno
since 1909 - decided to produce its own bikes under the marque name AJS (for
A.]. "Jack" Stevens, the dominant brother). Lightweights came first,
followed by the 698cc Model D V-twin, which debuted at the 1912 London Show. It
was the start of a long line that culminated in the 1000cc twin of the late 1930s.

Advanced
Design

The Model D
was a very advanced motorcycle for its day, with primary and final drive by
chain and a three-speed gearbox. The first versions had detachable heads, but
there were complaints about leaking cylinder joints, so fixed heads were
adopted in 1913.

Changed
Appearance

In 1915,
the displacement was increased to 748cc and the external appearance changed,
with the adoption of a vertical frame tube behind the engine and an elegant gas
tank enameled silver-gray and black. Detachable cylinder heads reappeared in
1916, but production of these models ended early that same year, as the big AJS
was not chosen for the British Army, and the firm had to manufacture munitions.
The big-twin did not reappear until the 1919 London Show. However, the British
Army did use a number of AJS V-twin power units in its 744cc Clyno machine-gun
outfits during WWI. In 1910, Clyno had moved into the former Stevens Screws
factory in Wolverhampton, where the father of their engine suppliers had traded
as a precision engineer.